While the effects of age on the adrenergic responsiveness of cardiac ventricular tissue has been delineated, data is scanty on how age may affect the cholinergic modulation of these adrenergic effects. Neither adrenergic nor cholinergic modulation of aged atrial tissue have been studied. Isolated transmural left atrial strips from adult (12 mo) and senescent (24) virgin male Wister rats were stimulated isometrically at Lmax at 30 degrees C in krebs buffer containing 0.5 mM Ca+. A dose response relationship to progressively greater concentration of isoproterenol (10-12 to 10-6M) was established for both groups. A progressive dose response relationship was similarly established for acetylcholine (10-10 to 10-3M) in atria superfused with Krebs already containing (10-6) isoproterenol. Changes in time to peak force, total developed tension, resting tension, contraction duration, and maximal rate of force development were measured. While age-related changes in time to peak force and contraction duration were found, an initial analysis of the data failed to show any age-related changes in adrenergic responsiveness as measured by these parameters. However, the developed tension in isoproterenol-potentiated senescent atria was more sensitive to suppression by acetylcholine.